Infrared laser diode wireless local area network

ABSTRACT

An infrared laser diode wireless local area network for communication between spatially dispersed terminals such as computers which may be located in a single room or in adjacent rooms. The lasers may be tuned to emit at varying frequencies for wavelength multiplexing, or a plurality of lasers each having a different output frequency can be connected with each terminal. A receiver connected to each terminal may similarly detect only a single narrow waveband or may detect a plurality of such wavebands. A transceiver may be employed for signal transmission between separate rooms. High speed data modulation of the carrier waves is provided with MOPA or similar lasers, and broad angular dispersion of the output is achieved by such lasers along with dispersive lenses.

This is a continuation of U.S. patent application No. 08/827,093, filedMar. 27, 1997 , now U.S. Pat. No. 6,025,942 which is a continuation ofU.S. patent application No. 08/317,889, filed Oct. 4, 1994, nowabandoned.

TECHNICAL FIELD

This invention relates to wireless local area networks for communicationbetween computers or other terminals.

BACKGROUND ART

Local area networks (LANs) typically provide for communication betweencomputer terminals located in the same room, building or complex ofbuildings by electronic connection between the terminals with conductivewires or optical fibers. Wireless communication between terminals usinginfrared (IR) light emitting diodes (LEDs) is known but suffers fromseveral drawbacks. One drawback of IR LEDs is a lack of connectivity atdistances over perhaps fifty feet that is caused by reduction of signalintensity to power levels inadequate to distinguish over ambient IRnoise. Another drawback is that of crosstalk between terminals, so thatinformation transmitted from a terminal is not clearly received byanother terminal.

Some prior art systems for infrared communication use mirrors to deflectthe light between stations. In U.S. Pat. No. 4,017,146, Lichtman teachesangular distribution of a concentrated laser beam by deflecting the beamwith a moving mirror so that the beam raster scans over a large angle.The beam impinges upon a given spatial location in short pulses thatamount to a small fraction of a given time period, the remainder of thetime period being essentially devoid of the beam at that location, andthus the transmission of data being similarly limited. U.S. Pat. No.4,982,445 to Grant et al. teaches a laser beam communication system forspacecraft utilizing mirrors positioned in the path of the beams whichadjust reflection to different angles.

Other systems employ high and low data transmission channels. U.S. Pat.No. 5,321,542 to Frietas et al. teaches an optical communications systemutilizing a high bandwidth, high speed infrared data channel along witha more robust, low bandwidth, low speed infrared channel for maintainingcommunication when the high speed channel is obstructed. U.S. Pat. No.5,229,593 to Cato teaches a free space laser communication systemoperating at a high power level for optimum data transmission when apath between terminals is not blocked, and operating at a lower,eye-safe power level when the path between terminals is obstructed.

Still other systems have characteristics that depend upon the medium oftransmission. U.S. Pat. No. 5,227,908 to Henmi teaches an intensitymodulated infrared signal for improved noise reduction transmission viaan optical fiber. U.S. Pat. No. 5,181,135 to Keeler uses light sourcestuned for minimizing losses in an under-water communications system.U.S. Pat. No. 5,159,480 to Gordon et al. teaches a communication systemfor naval vessels that sends out a horizontally dispersed, verticallyconcentrated infrared signal for receipt by a remote receiver.

Despite these advances in free space communication, certain obstaclesremain. Some known systems utilize a form of time multiplexing to avoidconfusion between signals from different terminals, thus cutting intothe time available for data transfer between separate terminals.Similarly, the frequency with which infrared diodes can be modulatedalso can limit the speed with which data can be transferred. Moreover,detection of the signals is often thwarted by ambient infrared noise.Furthermore, a free space local area network including terminalsdisposed in separate rooms has difficulties caused by walls separatingthe rooms. The term “free space” is meant to signify that a path throughair is available between terminals, although the path need notnecessarily be direct. For the situation in which walls substantiallyseal one room from another, a free space path is not present.

It is an object of the present invention to overcome the aforementionedobstacles.

SUMMARY OF THE INVENTION

The above object is accomplished by providing a wireless local areanetwork of separate terminals each of which has a connected transmitterand receiver. The transmitters include a laser diode with an angularlydispersed, narrow bandwidth infrared output, and the receivers have thecapability to detect infrared radiation at frequencies emitted by thetransmitters. Each terminal can send data to separate terminals bymodulating the output of its connected transmitter, and each terminalcan receive data from a separate terminal by demodulating radiationdetected by its connected receiver.

To avoid confusion between signals of different terminals, the infraredcarrier wavelengths transmitted by different terminals can be mutuallyexclusive, i.e. wavelength diverse. This wavelength diversity allows anincrease in the time during which data can be transmitted and received,since signals can be sent simultaneously between various transmittersand receivers rather than by time multiplexing the signals so that onlyone transmitter and one receiver are actively communicating at any giventime. The increase in signal time afforded by wavelength diversitybecomes more pronounced as the number of terminals in a network areincreased.

The speed of data transmission between terminals can alternatively beincreased by increasing the speed with which the transmitters can bemodulated. In this regard, laser diodes can be modulated at a muchhigher frequency than the light emitting diodes that are usuallyemployed for wireless networking. By employing amplitude modulation oflaser diodes, the modulation frequency can be in excess of a gigahertz.Due to this high modulation frequency, the terminals can be timemultiplexed rather than wavelength diverse, using a time multiplexingprotocol such as that offered under the trademark “Ethernet”. High poweroutput can be achieved with a low modulation current by modulating afraction of the gain region, such as with a master oscillator poweramplifier (MOPA) or flared resonant cavity laser diode.

The output signal from each transmitter is broadcast over a large areaat an intensity which can be detected by various receivers. This can beaccomplished, first, by limiting the bandwidth of the transmittedsignal, to facilitate detection of the signal over ambient noise.Second, the laser diode can be fashioned to have a high output powerthat is broadcast over a large area so that the intensity at anylocalized area is eye-safe, by employing lasers with flared outputs forhigh power, angularly dispersed beams. A dispersive lens can also bedisposed in front of the laser output with associated safety switchesthat terminate the output upon removal of the lens. Alternatively, afiber coupled laser diode or laser bar array coupled to an array offibers which are later either bundled or dispersed in space allow forsafe levels of light output intensity. A novel laser diode havingopposed flared outputs can be used for increased angular dispersion ofthe output. Output dispersion over a broad solid angle is generallydesirable for the networking of the present invention, a broad solidangle being defined in this application as at least 45° in any directionacross the beam that includes its axis.

For the situation in which free space transmission between terminalslocated in a single room is not possible, transmission schemes basedupon various net-working geometries are presented. For common corporateenvironments that have large rooms that are subdivided into cubicles bypartitions that extend partially to the ceiling to provide individualwork rooms, transceiving terminals mounted on the ceiling are employedto ensure data transmission between terminals in separate cubicles.Other buildings may have individual rooms but a mostly common crawlspace or attic above most of the rooms, and ceiling mounted transceivingterminals can again be employed, which communication between thosetransceiving terminals occurring via the crawl space. Still otherbuildings with individual rooms are connected by doors with access tocommon hallways, and transceiving terminals can be mounted adjacent thedoors, allowing communication via the hallways.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a system of the present invention havingseveral terminals with associated transmitters and receivers disposed ina room.

FIG. 2 is a plan view of a system of FIG. 1 including transceivers forcommunicating between terminals disposed in separate rooms.

FIG. 3 is a top plan view of a MOPA laser transmitter of FIG. 1 with anoutput shielded by a dispersive lens.

FIG. 4 is a top plan view of a flared resonant cavity laser transmitterof FIG. 1 with an output shielded by a dispersive lens.

FIG. 5 is a cutaway side plan view of a terminal of FIG. 1 having aplurality of lasers that each emit infrared light at a differentfrequency.

FIG. 6 is a top plan view of a dual flared MOPA laser transmitter ofFIG. 1 with outputs shielded by dispersive lenses.

FIG. 7 is a top plan view of a dual flared resonant cavity lasertransceiver of FIG. 2 with wavelength selective filters adjoininginput/output faces.

FIG. 8 is a perspective view of a frequency selective infrared receiverof FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIG. 1, a multi-terminal network of the presentinvention is shown disposed within a room 20. A first terminal 22 has aconnected transmitter 24 and receiver 26. The transmitter 24 contains atleast one laser diode which emits an angularly dispersed infrared outputrepresented by arrows 28. The output 28 has a narrow frequency bandcentered about a frequency F₁. A second terminal 30 has a connectedtransmitter 32 and receiver 34. The transmitter 32 contains at least onelaser diode that emits a broadly dispersed infrared output representedby arrows 36. The output 36 has a narrow frequency band centered about afrequency F₂. The frequency bands of outputs 28 and 36 are mutuallyexclusive. A third terminal 40 has a similar connected transmitter 42and receiver 44, the transmitter 42 having at least one laser diodewhich emits an angularly dispersed output represented by arrows 46 andwhich has a narrow frequency band centered about a frequency F₃, thatband exclusive of the frequency bands centered about F₁, and F₂.

In this embodiment, the terminals 22, 30 and 40 each have acharacteristic output frequency, F₁, F₂ and F₃, respectively, that actsto identify the terminal as well as avoid crosstalk between signals. Thereceivers 26, 34 and 44 each have means for detecting the outputfrequencies of the separate terminals and excluding other frequencies.The means for detecting certain frequencies while excluding others caninclude frequency specific filters disposed in front of photodetectorscapable of detecting low intensity level infrared light of anyfrequency. Alternatively, or photodetectors that are sensitive to onlyselected frequencies may be employed, as will be explained in moredetail later.

In another embodiment, the terminals can be identified by characteristicinput frequencies F₄, F₅, and F₆ detected by their receivers 26, 34 and44, respectively. Thus to send data from terminal 22 to terminal 30, thetransmitter 24 of terminal 22 would output signals at a carrierfrequency matching input frequency F₅. The transmitters 24, 32 and 42can be made to emit infrared light at the desired frequencies by severalmeans which will be discussed in greater detail below, including the useof multiple laser diodes connected to each terminal or the employment oftunable laser diodes.

In either of the above embodiments, the room 20 may be divided intoseparate working areas or cubicles by partitions such as wall 48 thatextends partially across the room 20. For this situation the terminal 30that is associated with an open portion of the room 20 may serve as abase terminal or relay station for other terminals that are separated bythe wall 48, such as terminals 22 and 40. A few bare terminals such asterminal 30 may be sufficient for networking a large room having manyindividual cubicles.

While free space networking within a single room can be relativelystraightforward, other network environments are more problematical. FIG.2 shows a network environment involving a first room 50 separated from asecond room 52 by a wall 54 which is impervious to infrared radiation. Apair of separate terminals 56 and 58 are disposed in the first room 50while another pair of terminals 60 and 62 are disposed in the secondroom 52. A free space area 64 adjoins both of the rooms across a wall66. The free space area 64 may be an attic or crawl space above therooms 50 and 52, or it may be a hallway next to the rooms 50 and 52separated from those rooms by doors, not shown, in the wall 66.

A first transceiver 68 is disposed in the wall 66 between the first room50 and the free space 64, and a second transceiver 70 is disposed in thewall 66 between the second room 52 and the free space 64. Thetransceivers 68 and 70 act as relays for signals between the first andsecond rooms 50 and 52. Each of the transceivers 68 and 70 has at leastone transmitter and at least one receiver on each side of the wall 66.Thus transceiver 68 has a receiver 72 and a transmitter 74 disposedwithin room 50, and a receiver 76 and transmitter 78 facing into thefree space 64, and transceiver 70 has a receiver 80 and a transmitter 82disposed within room 52, and a receiver 84 and a transmitter 84 disposedwithin free space 64. In operation, for example, a signal from terminal56 in room 50 is detected by receiver 72 of transceiver 68, which thenrebroadcasts the signal via transmitter 78 into free space 64 where itis detected by receiver 84 on transceiver 70. Transmitter 82 of thattransceiver 70 then rebroadcasts the signal by transmitter 82 into room52 to be detected by a receiver associated with terminal 62, which thendemodulates the signal to acquire data.

For the situation in which the free space 64 is a common hallway, thetransceivers 68 and 70 can be mounted adjacent to light switches thatare typically found on walls next to doors into the hallway. When thefree space 64 is an attic, an extension may be provided to thetransmitters and receivers disposed in the attic to allow protrusionabove insulation or other materials that may be found in the attic.Alternatively, the transceivers can be connected by wiring, so that thetransmitters and receivers disposed in the free space are not necessary.It is also possible to provide a transceiver, not shown, in the wall 54that separates adjoining rooms 50 and 52, for transmission directlybetween those rooms rather than via the free space 64. In each of thesesituations, additional transceivers can be added that serve as relays tolink additional terminals. The slight delay in the signals caused by therebroadcasting of the transceivers does not typically present a problemsince the transceivers allow infrared communication between regions thatare not otherwise in such communication.

In order to provide an angularly dispersed and high power output usinglimited modulation current, laser diodes having gain regions that areflared in one dimension such as a master oscillator power amplifier(MOPA) or flared resonant cavity laser are employed in the transmitters.Additional angular dispersion is provided by a dispersive lens or one ormore optical fibers. In general, a dispersion of output radiation overan angle of at least 45° in all directions from a central axis ispreferable for ensuring communication between terminals in a singleroom. Additional spatial dispersion may occur due to reflection of theradiation from walls and other objects.

In FIG. 3, a MOPA laser 90 is shown with a rod 92 disposed in front ofan infrared output of the laser 90. The rod 92 may be made of glass,plastic or other material that is translucent to the infrared output.This dispersive translucence can be achieved with microscopic scatteringparticles diffused throughout the rod 92, which may give the rod a milkyappearance. Alternatively, the rod 92 can have bends that act todisperse the output to divergent angles. The output radiation need notbe coherent for communication since the modulation frequency, which mayexceed a gigahertz, is still many orders less than the carrierfrequency. The rod 92 is held in a case 94 that has a safety switch 96pressing upon the rod 92. The laser 90 is powered by a power supply 98that is connected to the safety switch 96. Should the rod 92 be removedfrom the casing 94, the safety switch 96 operates to cut off the powerto the laser 90 and the output from the laser 90 is stopped.

The MOPA laser 90 has a gain region 100 which has several sections, eachof which has independent electrical connections so as to allowsubstantially independent generation of light emission conditions in thedifferent sections. The gain region 100 has a substantially uniformthickness in a direction normal to the plane of the paper of FIG. 3,that thickness being within a few orders of the wavelength of theinfrared output, and bordered by a cladding material to form a waveguidefor the light. As one example of materials that may be used for theinfrared MOPA laser 90, the gain region 100 and the cladding materialcan both be formed of epitaxially grown layers of InGaAsP, with the gainregion having a higher concentration of As than the cladding region. Theexact concentration of the elements in this compound can be used totailor the output wavelength to a desired value. A resonant cavity 102acts to reflect light emitted or passing through the cavity 102 byreflecting that light with a reflective wall 104 and distributed Braggreflector (DBR) gratings 106 and 108. A quantum well layer, not shown inthis figure, having a width and thickness equal to or smaller than thewavelength of light being reflected so that a single mode of light isconstructively reflected and amplified, may be present within the gainregion. The resonant cavity 102 is supplied with voltage for creating anelectron population inversion by a pair of opposed electricalconnections, a top connection 109 illustrated in this figure.

Some of the single mode light amplified in the resonant cavity 102 istransmitted beyond DBR grating 108 and into a flared portion of the gainregion 100. The flared portion could support multiple modes, but sinceit is being pumped with the single mode light from the resonant cavity102, the flared portion emits light of the same phase and frequency. Amodulation portion 110 of the gain region 100 is disposed in the flaredportion adjacent to the resonant cavity region 102 and has a topelectrical connection 112. The modulation portion 110 supplies anelectrical signal from a terminal, not shown in this figure, fortransmission of data from the terminal. A power amplification portion114 of the gain region 100 is broader than the other portions and hasthe capability to provide more amplified light due to having a largerarea available for electron population inversion. A top electricalconnection 116 provides voltage to the power amplification portion 114of the gain region 100. An output face 118 of the laser 90 has ananti-reflective (AR) coating, to maximize the transmission of the outputthrough the face 118. The MOPA laser 90 has the ability to producenarrow bandwidth coherent light that can be modulated with a low currentsignal and amplified to produce a powerful, angularly dispersed outputbeam. Such a laser 90 can be supplied with amplitude modulationsrepresenting data for transmission at a frequency exceeding 1 gigahertz.

FIG. 4 shows a similar laser 120 having a flared gain region 122 butlacking DBR reflectors. Instead, the entire gain region 122 of thislaser serves as a resonant cavity, with constructive reflectionoccurring from a very reflective back wall 124 and a partiallyreflective front face 126, as well as within the narrow separationbetween cladding regions in a thin, parallel portion 128 of the gainregion 122. Amplification and output light of this flared resonantcavity laser 120 is held to a single mode by the single mode ofconstructive reflection permitted in the parallel portion 128 and thelack of constructive reflection in a flared portion 130 of the gainregion 122 except for light reflecting from the front face 126 back tothe parallel portion 128.

Adjacent to the front face 126 of the laser 120 is a translucentdispersive lens 132 for broadcasting the output into a wide angularrange. The dispersive lens has a body 134 surrounding a bubble 136, thebubble 136 having a lower index of refraction for infrared light thanthe body 134. For example, the body 134 may be made of glass or plasticand the bubble 136 may be made of air or a less refractive glass orplastic. The bubble 136 is aligned with the output from the laser 120 sothat, due to the curvature of the bubble 136 at an interface with thebody 134, output light from the laser 120 is dispersed over broadenedangles. As discussed above, a safety switch presses upon the body 134,and removal of the lens 132 from the front of the laser 120 turns offpower to the laser 120, avoiding eye damage from an undispersed output.

Cleaved F-P cavity lasers can also be used as well as DBR or DFB lasers.These lase in a narrow enough band to achieve wavelength divisionmultiplexing in free space. Because they are simpler to fabricate thanthe MOPA they are likely to be preferred over the MOPA or flared cavitylasers. Electronically wavelength tunable DBR or DFB lasers areparticularly interesting because each transmitter can arbitrarilyaddress receiving terminals with tunable or fixed wavelength filters.

Either the MOPA laser 90 or the flared resonant cavity laser 120 can betuned to output different wavelengths of infrared light by adjustingparameters such as the current, voltage or temperature across the gainregion, thereby changing the size of the resonant cavity or theeffective wavelength within the resonant cavity due to changes in theindex of refraction of the gain region. Such methods for tuning laseroutput are known and will not be discussed in detail here. Thus a singlelaser can broadcast over different carrier frequencies. Alternatively, asingle terminal 137 can be connected with a plurality of diodes 138which each emit infrared light at a different output frequency, as shownin FIG. 5. In this situation, a single terminal can broadcast overdifferent carrier frequencies by selecting and providing power to aspecific laser 138.

Referring now to FIG. 6, a MOPA laser 140 having a gain region 142 withoppositely flared gain portions 144 and 146 at opposite ends of a thinparallel portion 148 has an advantage of broadcasting a powerful,coherent output in opposite directions through low reflectivity faces150 and 152. The parallel portion 148 is bordered by DBR reflectors 154and 156 that help to establish single mode amplification, but a similarlaser can be made without such reflectors that operates much like theresonant cavity laser 120 discussed above, provided that output faces150 and 152 are somewhat reflective. As discussed above with regard tosingle-output output lasers, dispersive lenses 151 and 153 arepositioned adjacent to or adjoining both faces 150 and 152.

A similar laser 157 shown in FIG. 7 can be employed as an opticaltransceiver by having an optical filter 158 adjoining an input-outputface 159, the filter 158 only allowing a selected narrow band ofwavelengths of infrared light to enter the a flared region 160 of thelaser 157, the band of wavelengths substantially matching the outputwavelength of the laser 157, the flared region 160 amplifying the lightadmitted through the filter 158. The filter 158 may be a Fabry-Perotinterference filter made of thin dielectric films of alternating highand low index of refraction materials having quarter wavelengththickness, except for a central half wavelength thick layer. A similarfilter 161 adjoins another input-output face 162 of the laser 153, sothat the only light admitted into the laser for amplification is that ofthe selected wavelength. Since the light of the selected wavelength isconstructively amplified, the filtered laser 153 acts to select andamplify the selected wavelength, acting as a repeater or relay forsignals sent at the carrier frequency corresponding with thatwavelength, without the necessity of electrical modulation. Since thelaser is optically pumped by the signals admitted into the gain region142, the laser 140 can rebroadcast those signals much more quickly thana transceiver that must convert optical signals to electronic signal andthen back to optical signals for rebroadcasting. Dispersive lenses, notshown, may be aligned in front of filters 158 and 161, the lenses actingto angularly broadcast the signals sent out from the laser whileconcentrating the signals received from outside the laser 153.Additionally, the lenses may be used to extend the length of atransceiver in order to bridge a wall between separate rooms. Whenrebroadcast of a signal is desired in a selected direction, the flaredregion facing that direction can be supplied with a higher voltage thanthe flared region facing oppositely and receiving the signal.

Referring now to FIG. 8, a photodetector 170 which can differentiatesignals of different carriers frequencies is shown with a low passfilter 172 adjoining a light receiving face 174 of the photodetector 170in order to screen out light of higher frequency than the infraredcarrier frequencies. The photodetector 170 is made from a series of PNjunctions of direct bandgap semiconductors having direct bandgapenergies corresponding to carrier frequencies. As discussed previouslywith regard to light emission, epitaxially grown layers of compoundscontaining InGaAsP can be selected to have appropriate bandgap energiesfor infrared light. A first layer 176 is p-type and a second layer 178is n-type semiconductor having a direct bandgap equal to the highestcarrier frequency desired to be detected. A photon having a frequencylow enough to pass through the low pass filter 172 and matching thebandgap of n-type layer 178 will be absorbed in layer 178 by causing anelectron in that layer to move to a conduction band from a valence band.An electrical current between leads 184 and 186 that are attached tolayers 176 and 178, respectively, represents a number of such electronsdue to a signal carried at the frequency corresponding to the bandgap oflayer 178. The leads 184 and 186 are connected to a terminal 187 whichreads data from the signals.

Photons having a frequency less than that of the bandgap of layer 178pass through that layer to reach a junction between p-type layer 180 andn-type layer 182, which is a direct bandgap material having a bandgapcorresponding to the next lowest carrier frequency. A pair of electricalleads 188 and 190 are connected to layers 180 and 182, respectively, tomeasure electrical current between layers 180 and 182. Thus photonsimpinging upon layer 182 having an energy corresponding to the lowestdirect bandgap of layer 182, generate conduction band electrons whichare measured as current or voltage representing a signal at that carrierfrequency. Terminal 187 acquires this signal and, due to the differentcarrier frequency than the signal from leads 184 and 186, acquires datathat may represent signals of a separate terminal. For clarity thisphotodetector is shown with only two carrier light absorbing PNjunctions, while many more such junctions may be employed in a devicefor detecting signals at many more carrier frequencies. Also, similardevices having PIN junctions rather than PN junctions may alternativelybe employed.

Alternatively, filters admitting different infrared frequencies may beused to select which carrier frequency is detected by a photodetectorreceiver such as a PIN diode. Fabry-Perot filters having thin layers ofdielectric films may be employed for this purpose, and the filters mayeach adjoin a separate photodetector associated with a terminal forreceiving data. Instead, various filters may all adjoin a singlephotodetector having the ability to differentiate which filter the lightpassed through. Thus, a receiver may be able to detect various carrierfrequencies, or may be specific in detecting only a certain, narrow bandof carrier frequencies, offering a means for identifying the receiver bythe frequencies it detects. This complements a previously discussedcapability of a transmitter of the present invention of selecting atransmission frequency from several available narrow-band channels oronly transmitting on a single, identifying channel.

What is claimed is:
 1. A network having a plurality of terminals in abuilding occupied by human beings, said network comprising: a firstterminal having a transmitter and a receiver, a second terminal which isremotely located from the first terminal, said second terminal having atransmitter and a receiver, each transmitter and receiver having anoptical centerline, the optical centerline of the first terminaltransmitter being offset from the optical centerline of the secondterminal receiver, and the optical centerline of the second terminaltransmitter being offset from the optical centerline of the firstterminal receiver; and each transmitter having a laser source forgenerating a laser beam, the laser beam from the first terminaltransmitter being of sufficient power and diverging from the lasersource at a sufficient angle to establish optical communication with thesecond terminal receiver despite misalignment therebetween, and thelaser beam from the second terminal transmitter being of sufficientpower and diverging from the laser source at a sufficient angle toestablish optical communication with the first terminal receiver despitemisalignment therebetween.
 2. The network of claim 1 wherein said lasersource contains multiple laser emitters.
 3. The network of claim 1wherein said laser source contains a plurality of lasers.
 4. The networkof claim 1 wherein said laser source is tunable to selected wavelengths.5. The network of claim 1 which further comprises: means, between eachlaser source and each receiver, for contacting the beam and causing itto diverge into free space in the building.
 6. The network of claim 1wherein each transmitter emits infrared light having a plurality ofdifferent wavelengths.
 7. A network having a plurality of terminals,said network comprising: a first terminal having at least a transmitter;a second terminal which is remotely located from the first terminal,said second terminal having at least a receiver; and said transmitterbroadcasting angularly dispersed optical signals from a laser diodesource into free space, said optical signals having sufficient power tobe sensed by the receiver in the second terminal, said transmitterincluding a dispersing device for angularly dispersing the beam from thelaser source over an angle of at least 45 degrees.
 8. The network ofclaim 7 wherein said dispersing device comprises translucent material.9. The network of claim 8 wherein said translucent material hasparticles dispersed within.
 10. The network of claim 7 wherein saiddispersing device comprises a lens.
 11. The network of claim 7 whereinsaid transmitter includes a safety switch for disabling the laser diodesource in the absence of the dispersing device.
 12. The network of claim7 wherein said laser diode source is tunable to selected opticalwavelengths.
 13. The network of claim 7 wherein said laser diode sourcegenerates a beam, said beam being angularly dispersed sufficiently toprevent damage to the eyes of persons within the free space.
 14. Thenetwork of claim 7 wherein said transmitter has means for modulatingsaid optical signals.
 15. The network of claim 7 wherein said receiverhas means for demodulating said optical signals.
 16. The network ofclaim 7 wherein the receiver further comprises: a photodetector; and afilter for filtering optical wavelengths from the photodetector.
 17. Thenetwork of claim 16 wherein said filter selectively passes wavelengthsassociated with the laser diode.
 18. The network of claim 7 wherein saidangularly dispersed optical signals have sufficient power to reflect offof at least one surface before being sensed by the receiver.
 19. Thenetwork of claim 1 wherein said laser beam is angularly dispersedsufficiently to prevent damage to the eyes of persons within thebuilding.
 20. The network of claim 1 wherein each transmitter has meansfor modulating said laser beam.
 21. The network of claim 20 wherein eachreceiver has means for demodulating said laser beam.
 22. The network ofclaim 1 wherein each receiver further comprises: a photodetector; and afilter for filtering optical wavelengths from the photodetector.
 23. Thenetwork of claim 22 wherein said filter selectively passes wavelengthsassociated with the laser source.
 24. A network having a plurality ofterminals in a building occupied by human beings, said networkcomprising: a first terminal having a transmitter and a receiver; asecond terminal which is remotely located from the first terminal, saidsecond terminal having a transmitter and a receiver, each transmitterand receiver having an optical centerline, the optical centerline of thefirst terminal transmitter being offset from the optical centerline ofthe second terminal receiver, and the optical centerline of the secondterminal transmitter being offset from the optical centerline of thefirst terminal receiver; and each transmitter having a laser source forgenerating a laser beam, the laser beam from the first terminaltransmitter being of sufficient power and diverging from the lasersource at a sufficient angle to establish optical communication with thesecond terminal receiver despite misalignment therebetween, and thelaser beam from the second terminal transmitter being of sufficientpower and diverging from the laser source at a sufficient angle toestablish optical communication with the first terminal receiver despitemisalignment therebetween; said terminals being located in differentrooms separated by a physical barrier; and a relay device forre-broadcasting optical information from a terminal in one room to aterminal in another room.
 25. The network of claim 24 wherein said laserdiode source generates a beam, said beam being angularly dispersedsufficiently to prevent damage to the eyes of persons within the freespace.
 26. The network of claim 24 wherein said transmitter has meansfor modulating said optical signals.
 27. The network of claim 24 whereinsaid receiver has means for demodulating said optical signals.
 28. Thenetwork of claim 24 wherein said relay device includes a relay laser.29. The network of claim 28 wherein said relay laser of said relaydevice is further comprised of an optical amplifier.
 30. The network ofclaim 24 wherein the receiver further comprises: a photodetector; and afilter for filtering optical wavelengths from the photodetector.
 31. Thenetwork of claim 30 wherein said filter selectively passes wavelengthsassociated with the laser diode.
 32. The network of claim 24 whereinsaid angularly dispersed optical signals have sufficient power toreflect off of at least one surface before being sensed by the remotereceiver.